1. Field of the Invention
The present invention relates to an imaging system, particularly, an imaging system for an optical engine of a projection apparatus. If one desires, a simple adjustment in the optical engine can result in a more precise focus and position of an output image.
2. Descriptions of the Related Art
Generally, there are two types of conventional internal projection systems; namely, a liquid crystal on silicon (LCOS) type and a digital light processing (DLP) type. Because of its high performance digital micromirror device (DMD) built into the DLP projection system, the DLP has become the more popular projection system of the two.
FIG. 1 shows a three-dimensional schematic view of a typical reflective digital light processing (DLP) projection apparatus. After a light beam for imaging is produced by an illumination system 190, it passes through a color wheel 191, emitting a light integration rod into a prism device 120. Both the light beam and imaging signals processed by a digital micromirror assembly (not illustrated), located under the prism device 120, pass through the prism device 120 and project onto a large size mirror (not illustrated) through a projection lens assembly 140. The image, as reflected from the mirror, is then projected onto a display screen. The prism device 120, the digital micromirror assembly, and the projection lens assembly 140, as a whole, are generally referred to as an imaging system 150.
FIG. 2 shows a planer schematic view of a typical transmissive DLP projection apparatus comprising a body 210, a projection lens assembly 240, and an illumination system 290. The DLP projection apparatus generates a light beam from the illumination system 290, while the body 210 projects a processed image onto a screen through the projection lens assembly 240. After a precise and delicate adjustment, the projection apparatus must be assembled very carefully to obtain a focused and precisely positioned image.
For example, the existing technology of adjusting the focus and the position of the image for a transmissive DLP projection apparatus is as follows: (1) provisionally fastening the illumination system 290 on one end of the body 210 with screws, (2) adjusting the position of the projection lens assembly 240 relative to the illumination system 290 step by step and with care to ensure proper focus and positioning of the image, and (3) screwing the projection lens assembly 240 on the body 210 with the tools. Understandably, many uncontrollable situations factor in during manual operation, as it indeed, takes time for the adjustment, positioning and fastening procedures. Moreover, when fastening the two machine parts with screws, the engaging force tends to change the previously well-adjusted distance, resulting in a shifted distance between the two parts. Therefore the output quality of the image of the projection apparatus is hard to control. In addition, as expected, applying the conventional manual adjustment and fastening procedures to the optical engine of a reflective DLP projection apparatus is even harder because the reflective DLP has more complicated structures than the structures of the transmissive DLP.
With the aforementioned limitations, the industrial field provides another way to adjust the focus and the position of the image with an adjustment fixture. The procedures are to assemble the projection lens assembly 240 on the body 210 with the screws, optimize the focus and the position of the image by adjusting the relative position of the illumination system 290 and the projection lens assembly 240 with the fixture, and then fix the relative position between the illumination system 290 on the body 210 by glue. Though the relative position of the illumination system 290 and the projection lens assembly 240 can be controlled by this measure, the adjustment fixture still needs to be designed individually. In addition, the procedure for operating the fixture during position adjustment is fairly complicated, thereby, resulting in longer adjustment time. Furthermore, the use of the specific, heat-resisting durable glue is very expensive and permanent. In other words, the relative position is impossible to adjust anymore once the glue is applied and cured. Overall, the cost for manufacturing and assembling a projection apparatus is not reduced.
As a result, the need for an improved imaging system structure that ensures a stable product quality for presenting an optimal output quality prior to factory release, becomes evident, as efficient procedures are desired to avoid complicated procedures, long operation time, high cost, and difficulty of controlling manufacture processes.